Alzheimer's researchers met with disappointment Monday when officials from Pfizer announced that the experimental drug bapineuzumab failed to improve dementia symptoms in a Phase 3 trial.

Lead investigator Reisa Sperling, M.D., told the New York Times that the experimental drug showed “no evidence at all of a clinical benefit of treatment on either of the primary measures, one cognitive and one functional,” compared to placebo. Three drug makers were jointly developing bapineuzumab: Pfizer, Elan and Johnson & Johnson

Scientists told the paper that bapineuzumab's failure, in addition to other recent drug failures, has raised doubts about whether beta- amyloid plaques — proteins in the brain that have been targeted by drug developers — are implicated in the progressive disease.

Earlier trials suggested that bapineuzumab is more successful in Alzheimer's patients a specific gene, called ApoE4, which raises the risk a person will get Alzheimer's disease and can make the disease worse. Trial results testing bapineuzumab in this population will conclude within the next couple months, according to the paper.